The present invention relates to a wind power generator that produces high output power of electricity by increasing wind flow speed.
Recently, in the field of power generation, wind power generators are attracting attention from such aspects as the breakaway from oil-based energy production and conservation of clean environment. Wind power generators, which utilize a natural wind flow, sometimes fail to produce sufficient wind power depending on geographical and weather conditions where generators are installed. Therefore, it has been suggested that by employing some means to generate sufficient power a weak wind flow is accelerated.
The present inventors have provided a wind speed-up device capable of efficiently increasing wind flow speed with a simple structure, which is disclosed in Unexamined Japanese Patent Publication No. 2002-213343. FIG. 8 is a longitudinal sectional view showing the wind speed-up device in Unexamined Japanese Patent Publication No. 2002-213343.
The wind speed-up device illustrated in FIG. 8 comprises a wind tunnel body 51 having a long cylindrical shape and expanding from an inlet 52 toward an outlet 53 through which wind flows. On an opening edge of the inlet 52 of the wind tunnel body 51 provided is an inlet shroud 55 opened outwardly with a curved surface. An opening edge of the outlet 53 is provided with a collar-shaped flange 56 that outwardly expands. An area adjacent to the inlet 52 is adopted for a position for outputting the generated wind power.
By the above structure, wind around a central axis of the wind tunnel body 51, flowing in from the front of the inlet 52, pulls in slow wind flowing along an inner wall surface of the wind tunnel body 51 and, on the rear side of the outlet 53, the wind around the central axis and wind flowing outside the wind tunnel body 51 pull in the slow wind flowing on the inner wall surface of the wind tunnel body 51, thereby obtaining a high-speed wind area adjacent to the inlet 52 inside the wind tunnel body 51 to output wind power.
By employing the above-described wind speed-up device to construct a wind power generator with a wind turbine for generating electricity disposed at a position for outputting wind power adjacent to the inlet 52, the wind turbine disposed at the position adjacent to the inlet 52 inside the wind tunnel body 51, which is a high-speed wind area in the wind tunnel body 51 of the wind speed-up device, can be efficiently rotated even by weak wind outside, which leads to a significant improvement in power generating ability as a wind power generator.
In the wind speed-up device of Unexamined Japanese Patent Publication No. 2002-213343, it is further suggested that the angle of inclination of a side wall portion against the axis of the wind tunnel body 51 be preferably in a range from 2 to 5 degrees. With the angle of inclination below 2 degrees, even when the ratio of the length of the wind tunnel body 51 to the diameter of the inlet 52 of the wind tunnel body 51 is increased, the effect of increasing the speed-up ratio tends to become smaller. With the angle of inclination above 5 degrees, the effect of pulling in the slow wind flowing on the inner wall surface of the wind tunnel body tends to become smaller. Accordingly, with a range from 2 to 5 degrees, the slow wind flowing on the inner wall surface of the wind tunnel body can be efficiently pulled in.
However, although the above-described wind speed-up device, when used as itself, has the greatest speed-up effect with a range from 2 to 5 degrees, the device provided with a wind turbine disposed for generating electricity adjacent to the inlet 52 of the wind tunnel body 51 has proven not to be most appropriate with the angle of inclination in a range from 2 to 5 degrees. This is because the wind turbine rotating within the wind tunnel body 51 has an influence on a wind flow passing through the wind tunnel body 51.
An object of the present invention is to provide a wind power generator having a wind turbine rotating inside a wind tunnel body, which can generate high output power by efficiently increasing wind flow speed.
A wind power generator according to the present invention is a wind power generator comprising a cylindrical wind tunnel body expanding toward a flowing direction of wind and a wind turbine for generating electricity disposed at a position adjacent to an inlet for a wind flow of the wind tunnel body, wherein an angle of inclination of a side wall portion of the wind tunnel body against an axis of the wind tunnel body is in a range from 5 to 25 degrees or, preferably, from 5 to 14 degrees.
FIGS. 1 and 2 show distribution of static pressure and wind velocity at positions from the front through the inside to the rear of the wind tunnel body. The horizontal axes in FIGS. 1 and 2 indicate a ratio obtained by normalizing a horizontal position X of which origin is the inlet of the wind tunnel body by length L of the wind tunnel body, where the direction of the outlet of the wind tunnel body is indicated as positive. The distribution of static pressure in FIG. 1 indicates the difference from the static pressure in a position free from influence of the wind tunnel body, and the vertical axis shows a ratio obtained by normalizing the difference in static pressure by dynamic pressure of approach wind velocity U∞. The vertical axis of FIG. 2 shows a ratio obtained by normalizing wind velocity U by the approach wind velocity U∞.
As shown in FIG. 1, with respect to the wind tunnel body disposed at an open space, the static pressure of wind both in front of the inlet and at the rear of the outlet is substantially equal to the static pressure of atmospheric pressure outside the wind tunnel body. In the case of the cylindrical wind tunnel body expanding toward a flowing direction of wind, as the static pressure inside the wind tunnel body increases in a direction toward the outlet as shown in FIG. 1, the pressure greatly drops around the inlet inside the wind tunnel body. Accordingly, wind flowing in from the front of the inlet into the wind tunnel body sharply accelerates around the inlet as shown in FIG. 2 and gradually decelerates toward the outlet while the pressure is recovered to become substantially equal to the static pressure of the atmospheric pressure at the outlet as shown in FIG. 1.
In other words, in the cylindrical wind tunnel body expanding toward a flowing direction of wind, wind has negative pressure and converges around a position on a slightly downstream side of the inlet inside the wind tunnel body, which provides an area of high-speed wind to output wind power thereat.
In a wind power generator of the present invention, a wind turbine for generating power is disposed at a position adjacent to the inlet of the wind tunnel body. Thus, resistance by the wind turbine itself can prevent separation of a wind flow on an inner wall surface of the wind tunnel body even if an angle of inclination of a side wall portion against an axis of the wind tunnel body is increased to more than 5 degrees. Furthermore, since rotation of the wind turbine accelerates flow rate of wind in a radial direction of the wind tunnel body, the wind flow on the inner wall surface of the wind tunnel body is further prevented from separating, and wind flowing in from the inlet of the wind tunnel body can smoothly flow along the inner wall surface of the wind tunnel body to the outlet. Therefore, even if the angle of inclination of the side wall portion is increased up to 25 degrees at the maximum, separation of the wind flow on the inner wall surface of the wind tunnel body can be prevented until the wind flow reaches the outlet.
When the angle of inclination of the side wall portion exceeds 14 degrees, separation of wind on the inner wall surface of the wind tunnel body shows a slight tendency to occur. However, with high-speed rotation of the wind turbine for generating electricity, the wind flow can be reattached to the inner wall surface of the wind tunnel body. Separation of wind can be thus controlled in a small range also in this case so that wind fed from the inlet of the wind tunnel body can flow smoothly along the inner wall surface of the wind tunnel body to the outlet.
Namely, in the wind power generator according to the present invention, wind fed from the inlet of the wind tunnel body can flow smoothly along the inner wall surface of the wind tunnel body to the outlet without causing separation of wind from the inner wall surface of the wind tunnel body. Therefore, the wind flow made to have negative pressure around the inlet of the wind tunnel body can recover pressure without a great flow loss until reaching the outlet, thereby efficiently accelerating wind velocity to generate high output power.
The optimal value of the angle of inclination of the side wall portion of the wind tunnel body varies depending on a resistance coefficient of the wind turbine. However, with the angle of inclination of the side wall portion ranging from 5 to 14 degrees, in particular, no separation of wind flowing along the inner wall surface of the wind tunnel body is generated at all as discussed above, which results in the maximum rate of pressure recovery, enabling most efficient acceleration of wind velocity to generate high output power.
With the angle of inclination below 5 degrees, where the efficiency of recovering pressure remains in a small value, negative pressure around the inlet does not increase enough to obtain great acceleration of wind around a position where the wind turbine is disposed. On the other hand, when the angle of inclination exceeds 25 degrees, separation of wind on the inner wall surface of the wind tunnel body occurs to cause a considerably large flow loss, which leads to lower efficiency of recovering pressure and failure to obtain large acceleration of wind.
In the wind power generator according to the present invention, it is preferable that the inlet of the wind tunnel body has a curved surface which smoothly expands toward an outside of the wind tunnel body or an upstream side of wind flowing in the wind tunnel body. By this structure, wind in the proximity of a front of the inlet of the wind tunnel body can be smoothly fed into the wind tunnel body, and the flow rate of the fed wind is increased in a radial direction by rotation of the wind turbine for generating electricity disposed adjacent to the inlet. Accordingly, separation of wind from the inner wall surface of the wind tunnel body around the inlet can be further prevented, realizing an area of high-speed wind more efficiently to generate high output power.
It is also preferable that the wind power generator of the present invention further comprises a collar-shaped brim formed on an outside of an opening edge of the outlet. By this structure, wind flowing outside the wind tunnel body collides with the collar-shaped brim and forms a strong vortex on a rear side of the collar-shaped brim, which causes low pressure around the outlet of the wind tunnel body. Therefore, it is possible to pull a stronger flow of wind into the wind tunnel body, thereby realizing an area of high-speed wind more efficiently to generate high output power.
Preferably, the collar-shaped brim has a width from 10 to 100% of a minimum inside diameter of the wind tunnel body. With a wind tunnel body having length larger than the minimum inside diameter of the wind tunnel body (that is, where the length of the wind tunnel body is L and the minimum inside diameter of the wind tunnel body is D, L/D greater than 1), when the width of the collar-shaped brim is increased to 50%, 75% and 100% in sequence, for example, a stronger vortex is generated on the rear side of the collar-shaped brim, which makes pressure around the outlet much lower than static pressure of atmospheric pressure. As a result, a force pulling the wind flow from the inlet becomes larger, which leads to acceleration of wind velocity around the inlet.
On the other hand, when the wind tunnel body has length smaller than the minimum inside diameter of the wind tunnel body, that is, L/D less than 1, an excessively large collar-shaped brim adversely blocks the wind flow and raises pressure on the upstream side by itself, thereby hindering wind from flowing into the wind tunnel body. Accordingly, when L/D is equal or close to 1, optimum width of the collar-shaped brim is approximately 50% of the minimum inside diameter of the wind tunnel body.